The invention relates to monitoring performance of downhole equipment.
In the production of oil and gas, the reliable operation of downhole equipment typically is of paramount importance. For example, one class of downhole equipment is actuator-based equipment that is used to displace downhole parts, such as pads and sleeves. To accomplish this, an actuator of the equipment may use, as examples, an electromechanical arrangement (an arrangement in which a motor actuates a screw drive, for example) or an electrohydraulic arrangement (an arrangement in which an electric motor is driven by a hydraulic pump or jack cylinder). Quite often, the actuator is used in a well process control application in which the consequences of failure may be potentially very expensive, as failure of the actuator may cause lost production, damage to the well, damage to the reservoir or abandonment of the well, as just a few examples.
A valve is one type of downhole equipment that may use an actuator. For example, a sleeve valve 10 (schematically depicted in FIG. 1) may include a linear actuator 9 to control the flow of well fluid from a producing formation into a central passageway of a production tubing 12. To accomplish this, the valve 10 may include a generally cylindrical sleeve 26 that closely circumstances the outside of the tubing 12. In the operation of the valve 10, a motor 14 (of the actuator 9) actuates a ball screw drive 20 (also of the actuator 9) to move the sleeve 26 to selectively restrict the flow of well fluid through radial ports 8 of the tubing 12.
Performance aspects of the linear actuator 9 may change over time, and unfortunately the actuator 9 may eventually fail. Therefore, it is often desirable for an operator at the surface of the well to know how the linear actuator 9 is performing in order to predict when the actuator 9 is going to fail. Without this knowledge, the operator may unexpectedly lose control of the valve 10 and thus, not be able to plan and take remedial actions (final positioning of the valve 10, as an example). As a result, production may be lost due to the unexpected loss of valve control. It may also be advantageous to observe the performance of the valve 10 for purposes of improving future valve designs.
One way to monitor the performance of the linear actuator 9 is to place circuitry (not shown) downhole to monitor selected parameters (of the actuator 9), such as voltages, currents, speeds and positions. When one or more of the monitored parameters fall outside of predefined limits, the downhole circuitry may transmit stimuli (signals on a bus, for example) uphole to indicate this event. A potential difficulty with this arrangement is that mere indication(s) of one or more limits being exceeded may not sufficiently describe the performance of the linear actuator 9 or provide advance warning of future problems. In other arrangements, downhole circuitry (not shown) may sample selected parameters of the linear actuator 9 at a predefined rate (a rate above the Nyquist rate, for example) so that a continual stream of information may be transmitted uphole that indicates different actual performance aspects of the actuator 9 in real time. However, this arrangement may consume a significant amount of the bandwidth that is available for communicating with downhole equipment.
Thus, there is a continuing need for an arrangement to address one or more of the difficulties described above.